When you're a Spartan, you have to train like one! Serena Williams took part in her first @spartan race this weekend, conquering it like everything else she does! Send her a 💪 if you train like the GOAT! (📸: @serenawilliams) #USOpen _ #wta #tennis #sports #serenawilliams #spartanrace #instaworkout #instatennis #tennisworkout